The FlexRay bus and the associated FlexRay protocol are described, for example, in European Patent No. EP 1 355 456 A1.
According to the FlexRay protocol, which operates using a time multiplexing method, frames or data transfer blocks are transmitted in a communication cycle having a static segment and/or a dynamic segment.
Here, the terms frame, data frame, data transfer block, communication, and message are used synonymously and identify the same thing.
A data transfer block contains a header segment (header), a data segment (payload), and a checksum segment (CRC data). A data segment contains one or more data units, which may also be of different sizes. The data transfer block is transferred from a first transceiver device or node, which is coupled to the FlexRay bus, to a second transceiver device or node, which is also coupled to the FlexRay bus.
A validity bit may be provided in each case to indicate whether current or obsolete data are being transmitted at the location of the corresponding data unit into the data transfer block. A validity bit set to one indicates that the corresponding data unit is valid. In contrast, a validity bit set to zero indicates that the corresponding data unit is invalid.
In any case, all validity bits of a data transfer block must be erased before renewed writing and subsequent transmission, to prevent invalid data units which have corresponding validity bits still having a one from being transmitted. A problem may arise in particular on the receiver side if it was not possible to erase a validity bit which was to have been erased in a timely manner before the transmission. Undetectable errors may arise in this way on the receiver side.